1. Field of the Invention
The present invention relates to thermosensitive recording materials and in particular relates to thermosensitive recording materials having excellent thermal response.
2. Related Art
Thermosensitive recording materials are generally composed of a substrate having provided thereon a thermosensitive recording layer containing as major constituents an ordinarily colorless or slightly colored dye precursor and an electron receptive developer. Upon being heated by means of a thermal head, thermal pen or laser beam, the dye precursor instantaneously reacts with the developer to form a recorded-image, as disclosed in Japanese Pat. Examined Publication Nos. 43-4160, 45-14039, etc. Because of the advantages of the relatively simple design of devices, ease of maintenance and making no noise, the recording devices employing such thermosensitive recording materials are being used in a wide field including recording instruments for measurements, facsimiles, printers, terminal devices for computers, labels, and automatic vending machines for railroad tickets and the like. Particularly in the field of facsimiles, demand for thermal sensitive devices has been greatly increased and the performance of facsimiles has been raised to high speed and the size of such devices has become very small due to reductions in transmission costs. Facsimiles have been reduced in cost and energy consumption has been lowered. In response to such high speeds and low energy performance required for facsimiles, high sensitivity has been demanded for thermosensitive recording materials. For high speed recording, formation of recorded images utilizing as high efficiency as possible small thermal energy liberated from a thermal head in very short time (generally less than 1 m sec) to color-forming reaction are necessary.
As a way to achieve the above-mentioned purpose the simultaneous use of a dye precursor and electron receptive compound capable of developing color of said dye precursor with a heat meltable substance having relatively low melting point as a coloring accelerator or a sensitizer has been proposed. It is proposed in Japanese Pat. application KOKAI (Laid-Open) Nos. 57-64573 and 58-87094 to use naphthol derivatives, Nos. 57-64592, 57-185187, 57-191085, 58-110289 and 59-15393 to use naphthoic acid derivatives, Nos. 58-72499 and 58-87088 to use ether or ester derivatives of a phenol compound.
However, thermosensitive recording materials produced by any one of the above methods are not still fully satisfactory in thermal response or the color-forming property.